Inside the Dirt – Bacteriophages

By Garlyn Colas

Dirt. Every day dirt that you walk by, walk on, and maybe even eat if you were that bold child who wasn’t afraid of anything. Well, dirt, you proved something to me today… that you have more things inside of you besides just bacteria and the random rock.

You have bacteriophages inside of you, which I didn’t know much about before this research project. I collected dirt from a dirt path that goes from the JHU campus to the neighborhood of Hampden to the west, and who knew that this would be the perfect breeding ground for bacteriophages.

I did not, especially after I tried to see if I had any bacteriophages through the method of Direct Plating. This method, for those who don’t know, is when I purify part of my dirt sample from the dirt and other unnecessary stuff and plate it on a Petri dish full of smeg bacteria to see if any phages were in my dirt sample. I would know by plaques, which is like a colony of phages, showing up on my plate and eating the yummy bacteria I had given it. Unfortunately, no plaques had shown up on my plate.

Fear not! Every good scientist goes through their highs and lows of an experiment, and I was no different. After Direct Plating, I tried to find phages through the method of Enrichment. Enrichment is when I give my phages, which can be small in number, a bunch of food and nutrients to grow and leave them to grow over night. The next day, I diluted and plated my enrichment sample to see if any plaques had shown up on my bacteria lawns. Sure enough, I saw nothing… as in NO BACTERIA! I looked at my other concentrations and saw that the lower the concentration, the more that I could make out the plaques that were affecting my plate. To make things even better, it looked like I had two different phages growing at the same time!

Now it was time to see if I really did have two different phages growing on my plate and, if they truly were phages, purify them from any bacteria or other phages that could get in their way. So I went through many rounds of streaking. I would touch one isolated plaque with a sterile stick and streak it in T – formation on a plate, which is meant to dilute the concentrated phages throughout the Petri dish. Then I would fill the plate with smeg and leave it overnight. After several streaks, it was apparent that I had 2 different kinds of phages: small, clear phages and big, cloudy phages that were hazy around the edges.

I had twins! I wish that I could have kept both of them and keep experimenting with both, but that would have been a lot of work. So I choose the small, clear phages to move on to the next step. Now that I had a purified phage, I needed to make lots and lots of it. Therefore, I made a “web plate,” which is a plate of highly concentrated phages. I did this by making a dilution series and plating them to see which would give me the best “web plate.”

After that, I put phage buffer into that plate and loaded it with Phage buffer to help it grow. I put all my new phages in a tube and diluted some of it to see approximately how many phages would be in that tube.

That is what I’ve been doing so far, which is much more than I originally thought I would. Still, I love working with bacteriophages and whenever I look at dirt now I can just picture the many more phages waiting to be discovered.

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